Filter choke with self-desaturating magnetic core



Sept. 5,1967 R. M. KELLER 3,340,458

FILTER CHOKE WITH SELF-DESATURATING MAGNETIC com; Filed June-16, 1964- 2Sheets-Sheet 1 INVENTOR. pk FoyIZ/ e fis I 6) g R. M. KELLER 3,340,458

FILTER CHOKE WITH SELF-DESATURATING MAGNETIC CORE Sept. -5, 1967 2Sheets-Sheet 2 Filed June 16, 1964 1 N VEN TOR. jjefler fir," for/7% iUnited States Patent 3,340,458 FILTER CHOKE WITH SELF-DESATURATINGMAGNETIC CORE Roy M. Keller, 707 Pine Drive, Torrance, Calif. 90501Filed June 16, 1964, Ser. No. 375,545 Claims. (Cl. 321-10) ABSTRACT OFTHE DISCLOSURE A filter choke including a magnetic core with anadjustable air gap, a first induction coil wound about the core, asecond induction coil wound about the core 111 inverted phaserelationship to the first coil, the coils having ends connected with acommon source of pulsating direct current, said air gap being set so thefrequency of oscillation is tuned so the ripple of the fields of thecoils are in 180 phase relationship and cancel each other out and equaland opposing magnetic fields are created in and through the corepreventing magnetic saturation of the core and so full permeability ofthe core material is available for amplification of alternating currentflux densities.

This invention relates to a filter choke and is more particularlyconcerned with a filter choke for removing the alternating currentcomponents or ripple, from rectified or pulsating direct current.

In electrical circuits where direct current is required and the powersource is alternating current, the alternating current is suitablyrectified. The direct current issuing from the rectifier is pulsating,that is, the current rises and falls in voltage, in a regular patternsimilar to a half sine wave of the alternating current power supply.Such a rise and fall of voltage is undersirable and oftentimesdetrimental. Accordingly, filtering and/ or choking means are employedto eliminate, reduce, or otherwise suitably alter the alternatingcurrent components or ripple to an acceptable form or condition.

There are several different kinds of filtering and/or choking means forthe above purpose, each of whichis particularly adapted for certainclasses or types of encuitry. One such means is the so-called filterchoke, WhlCl'l is, in essence, an induction coil through which thepulsating direct current is conducted. The rise and fall of voltage inthe current flowing through the choke creates an electromotive forcewhich opposes or buffers the voltage change in the direct current andthereby reduces or diminishes the pulse or ripple.

The ordinary filter choke involves an induction coil or winding about aniron core. The core is provided to in crease inductance of the coil byproviding a better and more concentrated path for the magnetic lines offorce generated by the coil.

The normal filter choke for direct current power supplies allows fordirect current saturation of the magnetic core. Because of the highuni-directional flux density or magnetic current, the effectivepermeability or magnetic amplification factor of the core and itsability to handle the inductive swing, is marginal.

An object of the present invention is to provide a novel filter chokeconfiguration wherein a pair of matched windings or coils, wound inopposite directions to have opposite polarity, are related to a commoncore, whereby the magnetic field generated by the coils and entering orpassing through the core are equal and opposite and tend to cancel eachother out, thereby desaturating or meterially reducing the magneticsaturation of the core material and rendering it more effective andavailable for amplification of the variable flux densities.

A further object of my invention is to provide an improved, moreeffective and more efiicient filter choke construction or configurationwhich can be made at a fraction of the physical size and weight ofconventional filter choke constructions of like ratings.

It is another object of this invention to provide a novel filter chokeof the character referred to wherein the effective swing is materiallyincreased, as compared with conventional choke constructions of likephysical size and weight, whereby the size and weight of the capacitorsnormally associated with such constructions to eliminate or reducevoltage surge, can be materially reduced in size and rating, or are notsubject to overloading and the like.

Still another object of this invention is to provide an improved andmore effective filter choke construction of the character referred toabove wherein the bleeder current requirements, to prevent voltagesoaring, are materially reduced.

It is an object of my invention to provide a filter choke constructionwherein the cycle fundamental ripple factor and the even, in phase, 240cycle harmonic or component are cancelled out, leaving only the 360cycle harmonics, or component of the ripple. Accordingly, the output ofthe choke provided by this invention contains a 360 cycle ripple factoras distinguished from a conventional choke construction wherein theoutput contains a 120 cycle output and is therefore three times aseffective as a conventional choke.

When conventional filter choke constructions are cascaded or arranged inseries, their effectiveness is increased by a standard multiplicationfactor, that is, by the square. An object of this invention is toprovide a novel, improved and more effective filter choke constructionof the character referred to which is three or more times efiective thanconventional choke constructions and is such that when cascaded orarranged in series, their eifectiveness is increased by at least thecube.

It is another object of this invention to provide a novel two sectionfilter choke construction or configuration wherein each section isestablished in accordance with my basic core and coil configuration andin which certain or selected coils are inverted to vary and control theeffect of the construction, whereby output requirements ranging fromconstant voltage output to constant current output can be advantageouslyprovided.

The various objects and features of my invention will be fullyunderstood from the following detailed description of a typicalprefer-red form and application of my invention throughout whichdescription reference is made to the accompanying drawing in which:

FIGURE 1 is a circuit diagram of my new choke configuration;

FIGURES 2, 3 and 4 are diagrammatic views of other embodiments of myinvention;

FIGURE 5 is a diagrammatic view of one structural embodiment of myinvention;

FIGURE 6 is a diagrammatic view of another structural embodiment of myinvention.

The basic filter choke configuration that I provide as illustrated inFIGURE 1 of the drawings, involves a magnetic core B of suitablematerial and design and two coils L and L electrically isolated andwound about the core B. The coils L and L are wound in oppositedirections whereby the polarity of their induced magnetic fields areopposite to each other.

The coil L is connected between the positive side of a rectifier system10 and the positive side of a filter capacitor C, while the coil L isconnected between the negative sides of the rectifier system andcapacitor C.

The rectifier receives 60 cycle alternating current from a suitablepower source, such as a generator 12, and puts out direct cur-rent witha 120 cycle ripple or alternating current component. The output of thechoke flows to a suitable resistance load 13, in accordance with normalpractice and as illustrated in the drawings.

The pulsating direct current passes through the coils L and L in such afashion as to develop opposite and opposing, equal magnetic fields. Bysuitably adjusting the air gap of the core, in accordance with standardtechniques, the frequency of oscillation is changed and tuned so thatthe 120 cycle ripple of the two fields of opposite polarity are in 180phase relationship. Accordingly, the 120 cycle ripple factors and theeven, 240 cycle component of said ripple are cancelled and only the 360cycle component of the ripple, which is uneven and 180 out of phase withthe even 120 and 240 cycle components are established or remain.Further, the magnetic core B is desaturated and the full magneticamplification factor or permeability thereof is available foramplification of the remaining 360 cycle alternating current fluxdensities.

As an example of the effect of the configuration that I provide, if tenamperes direct current is passed through :a one turn coil about a coreof one cubic inch, the increased permeability of 29 gage, 3.6% siliconsteel is 300 When flux density for alternating current is 2,500Maxwells. If the direct current saturation is eliminated, thepermeability becomes 5100. This results in a gain of usefulness of thesteel by a factor of 5100 divided by 300, or 17 times.

Due to the increase in effective permeability of the core B, the numberof turns necessary to provide the same inductance is decreased by afactor similar to the square root of 17, or about 4, with a consequentreduction in copper resistance and a shortening of the magnetic path fora further increase in inductance.

It will be noted that if the original physical size of the inductancechoke is maintained, a reduction of the size of the filter capacitor Cis allowed.

It will be further noted that since transformer utilization factors areincreased by choke input, in an equivalent complete circuit, thetransformer and the choke may be reduced to approximately one-thirdnormal size.

FIGURE 2 of the drawings is a diagram of a two section filter chokeembodying the present invention. The set-up or configuration now underconsideration includes a first section X and a second section Y. Thefirst section X involves a core B and a pair of coils L and L relatedthereto. The section X is connected with the plus and minus sides of arectifier 10 receiving current from a generator 12 and with a capacitorC', similar to the configuration shown in FIGURE 1 of the drawings.

The second section Y includes a core B coils L and L and a capacitor CThe coils L and L are connected in series with the coils L and L of thefirst section X. The output side of the section Y is connected with asuitable resistance 13.

It will be apparent that if the matched coils L L and L L were wound inlike directions, all in series, the cores B and B would not bedesaturated and the 120 cycle ripple in the magnetic fields would notcancel each other out. Rather, the cores would be saturated and the 120cycle ripple or alternating current component would remain in theoutput.

Such a set-up would be no more than a pair of cascaded, conventionalfilter choke constructions. The cores would store voltage and theresulting set-up would constitute a tapped storage inductor.

If coil L is inverted, as illustrated in FIGURE 2 of the drawings, thecore B is desaturated and the 120 cycle ripple and its even 240 cyclecomponent are cancelled. Core B would have no storage effect. The secondsection of this set-up receives the 360 cycle output from the firstsection. Since the coils L and L are not inverted relative to eachother, the second section provides storage effect. Accordingly, theconfiguration shown in FIGURE 2 provides increased capacitance plusfilter storage through voltage feed back action.

It will be apparent that if coil L was inverted instead of coil L thesame effect would be accomplished.

With the same, basic, two section configuration, if neither coil L or Lwere inverted and coil L in the second section Y was inverted, asillustrated in FIGURE 3 of the drawings, the first section of the set-upwould have storage effect and its output to the second section Y wouldhave cycle ripple. The second section would cancel out the 120 cycleripple and its even 240 cycle component and its output would containonly the 360 cycle harmonic of the AC component, which would beeffectively choked. This set-up would provide energy storage plusvoltage feed back of alternating current components not desired in theoutput and would be particularly serviceable in constant voltage outputpower supplies. The choke action of the input section is enhanced by thevoltage feed back of the second section.

It will be apparent that if L was inverted, instead of L the resultingset-up would have the same effect as that illustrated in FIGURE 3 anddescribed above.

With the same, basic two section configuration as set forth above, ifone or the other of coils 1 and 2 and one or the other of coils 3 and 4were inverted relative to its related coil, both the first and thesecond sections X and Y would provide voltage feed back and there wouldbe no storage effect in the resulting structure.

In FIGURE 4 of the drawings, I have illustrated coils 1 and 3 invertedrelative to their related coils 2 and 4, in accordance with the above.

With a configuration as set forth above and as illustrated in FIGURE 4of the drawings, a capacitive filter with voltage feed back is provided.This form of choking provides a constant current power supply.

In FIGURE 5 of the drawing I have illustrated, diagrammatically, atypical embodiment of my invention.

The structure includes a AAIOS-Arnold core B. The several coils L L Land L are alike and matched. For example, the coils consist of 1500turns each of No. 22 heavy Formar, good to at least 850 v. AC input tobridge rectifier and one ampere current. The filter capacitors C and Care alike and rated at 15 UP.

The weight of the structure disclosed and set forth above would be lessthen ten pounds.

The effective inductance of this structure as a choke input filter isthe same as two series chokes of 1.36 henries each, 400 volts, 1 ampereoutput at 0.425% ripple (360 cycle). The core separation at L and L isabout of an inch, while the separation between L and L is minimal. Theair gap on each side is approximately 0.023 inch.

In the above structure there is storage effect.

Employing the same basic structure as set forth above, but inverting Lrelative to L and changing the phase thereof for capacity input,requires a 1 /2 inch air gap for 0.27% ripple at 1 ampere, 400 v. DC.This results in the equivalent of two 1.67 henry chokes and utilizesabout two-thirds of the core.

Reducing coils L and L to 500 turns each gives 0.5 v. r.m.s. or 0.125%ripple at 400 volts direct current, 1 ampere output. At A inch air gap,effective inductance is 2.4 henries at each coil. I

Making coils L and L 1000 turns each, the air gap on the plus sideinches and the air gap on the minus side of an inch, minimum separationof coils on the lower or minus side and maximum on the other or plusside (1 ampere, 400 v. db out and 0.035% ripple, the effective inductiveaction of each coil is about 4.25 henries. In this set-up, there is nostorage action and the back EMF elfect of the transformers is used tobuck the voltage ripple frequency.

It is to be noted that the first capacitor C acts as a phase shiftnetwork as in any transmission line. The output capacitor C acts as thetermination.

It will be noted that an increased air gap increases tolerance tocapacitance variations.

As is illustrated in FIGURE 6 of the drawings, the present invention canbe advantageously employed or established with a standard E core. Forexample, an Arnold R-100 square stack core B, with about 1500 turns ofNo. 29 wire on each of three legs and connected as illustrated in FIGURE6 of the drawings, produces the equivalent of 14 henries inductance withstorage capacity and is rated at ampere.

From the foregoing, it will be apparent that I have invented a new andimproved filter choke configuration or construction which is highlyelfective and dependable in operation and which makes possible theestablishment of filter choke components that are a fraction of thesize, weight and cost of conventional filter choke configurations oflike rating.

Having described only typical preferred forms and applications of myinvention, I do not wish to be limited to the specific details hereinset forth, but wish to reserve to myself any modifications andvariations that may appear to those skilled in the art and which fallwithin the scope of the following claims.

Having described my invention I claim:

1. A filter choke of the character referred to including a firstinduction coil wound about a magnetic core with a set air gap, a secondinduction coil about the magnetic core and wound in inverted phaserelationship to the first coil, said coils having ends connected with asource of pulsating direct current, and create equal and opposingmagnetic fields in and through the magnetic core preventing magneticsaturation of the core, so the full permeability of the core material isavailable for amplification of alternating current flux densities.

2. A filter choke of the character referred to including a magnetic corewith a set air gap, a first induction coil Wound about the core andhaving one end connected with a source of pulsating direct current andits other end connected with one side of a filter capacitor and having alead to connect with one side of a resistance load, a second inductioncoil wound about the magnetic core in phase opposition to the first coiland having one end connected with the source of pulsating direct currentand its other end connected with the other side of the filter capacitorand having a load connected with the other side of the resistance load,the air gap being set so the frequency of oscillation is tuned so theripple of the fields of the coils are in 180 phase relationship and soequal and opposing magnetic fields are created in and through themagnetic core, resulting in desaturation of the magnectic core wherebythe full permeability of the core material is available foramplification of alternating current flux densities.

3. A filter choke of the character referred to including a magnetic corewith a set air gap, a first induction coil Wound about the core andhaving one end connected with the positive side of a rectifier and itsother end connected with the plus side of a filter capacitor and havinga lead to connect With the plus side of a resistance load, a secondinductance coil wound about the core in inverted phase opposition to thefirst coil and having one errd connected with the minus side of therectifier and its other end connected with the minus side of the filtercapacitor and having a lead connected withthe minus side of theresistance load, the air gap being set so the frequency of oscillationis tuned so :the ripple of the fields of the coils are in 180 phaserelationship and; whereby equal and opposing magnetic fields are createdin and through the core resulting in desaturation of the magnetic core,so the full permeability of the core material is available foramplification of alternating current flux densities.

4. A filter choke of the character referred to including an E-shapedmagnetic core, a first induction coil wound about one outside leg of thecore, a second induction coil wound about the other outside leg of thecore, and a desaturating ripple bucking coil wound about the center legof the core, each outside core being connected to one polarity of therectifier system on the input and to a like polarized capacitor at itsoutput, the center leg coil connected in desired polarity to one or theother of the input coils and thence to an output capacitor and to adirect current load.

5. A structure as set forth in claim 1 wherein said ends of the coilsare connected with a source of rectified 60 cycle alternating currentand said air gap is set to the sixth harmonic of the 6:0 cycle inputcurrent, so the fundamental cycle ripples and the even 240 cyclecomponents thereof, in the two coils, are in phase relationship andcancel each other out and the unevened 360 cycle components are in 360phase relationship and are cumulative in effect.

6. A structure as set forth in claim 2 wherein said one end of the coilis connected with a source of rectified 60 cycle alternating current andsaid air gap is set to the sixth harmonic of the 60 cycle input current,so the fundamental 120 cycle ripples and the even 240 cycle componentsthereof, in the two coils, are in 180 phase relationship and cancel eachother out and the uneven 360 cycle components are in 360 phaserelationship and are cumulative in effect.

7. A structure as set forth in claim 3 wherein said rectifier isconnected with a source of 60 cycle alternating current and the air gapis set to the sixth harmonic of the 60 cycle input current, so thefundamental 120 cycle ripples and the even 240 cycle components thereof,in the two coils, are in 180 phase relationship and cancel each otherout and the uneven 360 cycle components are in 360 phase relationshipand are cumulative in effect.

8. A filter choke of the character referred to including, a firstmagnetic core, matched first and second induction coils wound about thefirst core, the first coil having one end connected with the positiveside of a rectifier receiving 60 cycle alternating current, and itsother end connected with the positive side of a first filter capacitor,the second coil having one end connected with the negative side of therectifier and its other end connected with the negative side of thefirst filter capacitor, a second core, matched third and fourthinduction coils wound about the second core, the third coil having oneend connected with the positive side of the first condenser and itsother end connected with the positive side of a second condenser, thefourth coil having one end connected to the negative side of the firstcondenser and its other end connected with the negative side of thesecond condenser, and a resistance load connected between the sides ofthe second condenser, one of the coils related to the first core beingwound in inverted phase relationship to its related coil whereby themagnetic fields induced by said coils are of opposite polarity andcancel each other to prevent saturation of the related core and renderit available for amplification of alternating flux densities, saidrelated core being adjusted whereby the 120 cycle fundamental ripplefrequencies and their even 240 cycle components in the magnetic fieldsof said related coils are in phase opposition and are cancelled out andwhereby the even 360' cycle components are in phase and are cumulative.

9. A filter choke of the character referred to including, a firstmagnetic core, matched first and second induction coils wound about thefirst core, the first coil having one end connected with the positiveside of a rectifier receiving 60 cycle alternating current, and itsother end connected with the positive side of a first filter capacitor,thesecond coil having one end connected with the negative side of therectifier and its other end connected with the negative side of thefirst filter capacitor, a second core, matched third and fourthinduction coils Wound about the second core, the third coil having oneend connected with the positive side of the first condenser and itsother end connected with the positive side of a second condenser, thefourth coil having one end connected to the negative side of the firstcondenser and its other end connected with the negative side of .tlhesecond condenser, and a resistance load connected between the sides ofthe second condenser, one of said coils related to the second core beingwound in inverted phase relationship to its related coil whereby themagnetic fields induced by said coils are of opposite polarity andcancel each other to prevent saturation of the related core and renderit available for amplification of alternating flux densities, saidrelated core being adjusted whereby the 120 cycle fundamental ripplefrequencies and their even 240 cycle components in themagnetic fields ofsaid related coils are in phase opposition and are cancelled out andwhereby the even 360 cycle components are in phase and are cumulative.

10. A filter choke of the character referred to including, a firstmagnetic core, matched first and second induction coils wound about thefirst core, the first coil having one end connected with the positiveside of a rectifier receiving cycle alternating current, and its otherend connected with the positive side of a first filter capacitor, thesecond coil having one end connected with the negative side of therectifier and its other end connected with the negative side of thefirst filter capacitor, a second core, matched third and fourthinduction coils wound about the second core, the third coil having oneend connected with the positive side of the first condenser and=itsother end connected with the positive side of a second condenser, thefourth coil having one end connected to the negative side of the firstcondenser and its other end connected with the negative side of thesecond condenser, and a resistance load connected between the sides ofthe second condenser, one of the coils related to each of the coresbeing wound in inverted phase relationship to its related coil wherebythe magnetic fields induced by said coils are of opposite polarity andcancel each other to prevent saturation of the cores and render thecores available for full amplification of alternating flux densities,the said related cores being adjusted whereby the cycle fundamentalripple frequencies and their even 240 cycle components in the magneticfield of said related coils are in phase opposition and are cancelledout and whereby the uneven 360 cycle components are in phase and arecumulative.

References Cited UNITED STATES PATENTS 2,893,939 7/1959 Reid 333-79FOREIGN PATENTS 29,466 8/ 1925 France. 855,421 11/1952 Germany.

JOHN F. COUCH, Primary Examiner.

W. H. BEHA, Assistant Examiner.

1. A FILTER CAKE OF THE CHARACTER REFERRED TO INCLUDING A FIRSTINDUCTION COIL WOUND ABOUT A MAGNETIC CORE WITH A SET AIR GAP, A SECONDINDUCTION COIL ABOUT THE MAGNETIC CORE AND WOUND IN INVERTED PHASERELATIONSHIP TO THE FIRST COIL, SAID COILS HAVING ENDS CONNECTED WITH ASOURCE OF PULSATING DIRECT CURRENT, AND CREATE EQUAL AND OPPOSINGMAGNETIC FIELDS IN AND THROUGH THE MAGNETIC CORE PREVENTING MAGNETICSATURATION OF THE CORE, SO THE FULL PERMEABILITY OF THE CORE MATERIAL ISAVAILABLE FOR AMPLIFICATION OF ALTERNATING CURRENT FLUX DENSITIES.